The present invention relates to lighting fixtures of the type mounted in suspended ceilings and, in particular, to a housing structure of the fixtures.
A conventional lighting fixture adapted to be mounted in a suspended ceiling is depicted in FIGS. 11 and 2. That fixture 10 includes a metal housing 12 in which one or more fluorescent lamps 14 are mounted Also mounted in the housing is shielding media in the form of a deep cell parabolic louver assembly 16 for directing the emitted light in a desired fashion.
The housing 10 comprises two transverse end plates 18 (only one being shown in FIG. 1) which are suitably affixed (e.g., by bolts or rivets) to the central housing section 20. Each end plate includes a lower transverse support flange 17 forming a downwardly facing transverse surface 21. The central housing part 20 includes a pair of longitudinal walls 22 which include bottom support flanges 23 forming downwardly facing, longitudinal surfaces 24. The fixture 10 is installed within a suspended ceiling 28 (see FIG. 2) which comprises horizontal grid members 30 that support ceiling tiles 32. The surfaces 21, 24 of the bottom flanges are seated upon bearing surfaces formed by horizontal legs 33 of the grid members 30.
It is highly desirable that the fixture be installed such that the lower edge or aperture 40 of the louver assembly is nearly coplanar (i.e., flush) with the undersides 42 of the ceiling tiles. That goal is complicated by the fact that grid members of various sizes are commonly employed in the ceiling industry. For example, so-called "screw slot" grid members 30 depicted in FIGS. 2 and 12 have a leg height H of 0.312 inches, whereas so-called "standard" grid members 30', depicted in FIG. 11, have a leg height H, of 0.050 in. Therefore, it will be appreciated that a fixture in which the vertical relationship between the bottom surfaces 24 of the support flanges and the aperture 40 of the louver assembly is dimensioned so as to be compatible with one type of grid member, will not be compatible with the other type of grid member.
Attempting to deal with this problem by simply raising and lowering the louver assembly 16 within the housing is not satisfactory, because that changes the vertical focal/light center spacing between the lamp 14 and the louver assembly 16, and thus will adversely affect the photometric relationship between the lamp and the parabolic cells of the louver assembly. The provision of louver assemblies of different heights which can be interchanged in the housing to maintain a constant spacing S, will not solve the problem, because the difference in parabola heights will also adversely affect the photometric characteristics of the optical assembly.
Therefore, it would be desirable to provide a lighting fixture which can be easily and inexpensively adapted to different size grid members while maintaining a desired spacing between the lower edge of the shielding media and the lamp(s).
It would also be desirable to provide such a lighting fixture which can be adapted to different size grid members by the end user of the lighting fixture.